The traditional method used to protect roofs from rain and other forms of inclement weather was to lay down several layers of material, normally felt soaked with bitumen, thereby building up a waterproof membrane. This method has several problems; the process is very long and susceptible to contamination by rainwater or other foreign materials. Furthermore, the bitumen must be heated to the point where it gives off noxious odors.
In recent years, alternate systems using elastomeric membranes have become increasingly popular. A suitable elastomeric membrane is laid over the top surface of the roof itself, or more preferably, an insulation board. A variety of methods for fastening the elastomeric membrane to the surface of the roof have also been developed. One method is to spread an adhesive over the entire surface of the roof before laying down the membrane. This process is very labor-intensive and requires that the installers be exposed to adhesives giving off noxious fumes.
Alternatively, the membrane can be fastened to the roof mechanically. Several devices have been developed which require that a nail or screw be allowed to penetrate the membrane. This can lead to tears and rips in the membrane, especially as the membrane expands and contracts in response to changes in the ambient temperature. These breaches in the integrity of the membrane in turn can lead to water leakage and eventual damage to the underlying roof.
A variety of other devices have also been developed which are capable of securing a membrane to the upper surface of a roof without penetrating the membrane. The applicant believes that the following references are illustrative of the non-penetrating anchoring systems which have been patented.
______________________________________ U.S. Pat. No. Patentee ______________________________________ 4,519,175 Resan 4,617,771 Tomaszewski 4,624,092 Baginski 4,631,887 Francovitch 4,658,558 Verble ______________________________________
U.S. Pat. No. 4,519,175 issued to Resan discloses a three-piece fastening apparatus wherein the roofing membrane is laid over the bottom piece and then a second tined piece is clipped over the membrane and the protruding boss of the bottom piece. The top piece of the device is then screwed onto the second piece thereby locking the device together and securing the membrane.
U.S. Pat. No. 4,617,771 issued to Tomaszewski discloses a three-piece fastening system which snaps together. The device includes an elastic ring which provides tension when a top piece is snapped into the bottom piece.
U.S. Pat. No. 4,624,092 issued to Baginski discloses a two-piece fastening system which snaps together. The bottom piece of the device serves as the male element; the membrane is laid over the bottom piece, and a collar is snapped over the top of the bottom piece. This device, however, allows the area of the membrane directly over the bottom piece to be exposed to the atmosphere.
U.S. Pat. No. 4,631,887 issued to Francovitch discloses a three-piece fastening system which snaps together. In the use of this device, a second piece is inserted inside of the bottom piece which helps maintain the tension produced when the top, or cap piece is snapped over the membrane and the protruding boss of the bottom piece.
U.S. Pat. No. 4,658,558 issued to Verble discloses a two-piece fastening system which snaps together. In this device, the bottom piece serves as the female piece. The bottom piece is attached to the top surface of the roof, the membrane is laid out, and the top piece is snapped into the bottom piece, thereby locking the device together and securing the membrane.
These devices are all capable of securing an elastomeric membrane to the upper surface of a roof without penetrating the membrane; however there are several limitations and suboptimizations inherent in these devices and the prior art in general.
First and foremost, the way in which previously-disclosed devices generate the restraining force necessary to secure the membrane to the roof creates problems. For example, devices which screw together, such as the device disclosed by Resan in U.S. Pat. No. 4,519,175, carry with them the danger that the device will be over-tightened, thereby straining or even ripping the membrane. Alternatively, devices which screw together may be undertightened, allowing the top, or cap piece of the device to work its way loose.
Devices which utilize the thickness of the membrane itself to generate the majority of the restraining force used to hold the device together, and hence, anchor the membrane to the roof have other problems associated with their use. Devices such as those disclosed by Verble in U.S. Pat. No. 4,658,558 and Francovitch in U.S. Pat. No. 4,631,887, in essence, call for the installer to provide the wedging force necessary to either push a cap over a protruding boss, as in the case of Francovitch, or to push a plug into a housing, as in the case of Verble. These types of devices can stretch and fatigue the membrane, increasing the risk that a rip will form which allow water to pass through the membrane and damage the underlying roof structure. Furthermore, fastening devices which employ the thickness of the membrane itself to supply the majority of the tensional force necessary to keep the device locked together have very little margin for error. For example, the calender seams formed where two sheets of the roofing membrane are joined together are often too thick to fit into these types of devices. This can lead to either the necessity for careful pre-planning of the placement of the devices or wastage of those bottom pieces which are installed too near a calendar seam. Also, devices of this type which utilize base plates which are basically circular may give rise to a large number of irregularly-distributed wrinkles which give the impression of a slovenly installation.
A second major problem with the devices disclosed by the existing patents is the difficulty in servicing these devices. After a elastomeric membrane has been installed on a roof, it may become necessary to inspect the membrane for a variety of reasons; for example when a water leak is discovered inside the underlying structure. With the previously-patented fasteners, it is almost impossible to disassemble the fastening system without damaging both the device and the membrane.